The present invention relates to heat absorbing devices and a method for constructing same. Said heat absorbing devices have heat absorbing chemicals, i.e. endotherms, which use their respective heats of reaction to cool and maintain and control the temperature and heat of heat sensitive devices. These endotherms comprise certain acids and their salts, certain bases and their salts, and certain organic compounds, which have never before been used in the manner described, disclosed and claimed below.
Often, active cooling of such electronic components, particularly delicate TR modules, Impatt diodes, data recorders, containers for chemicals and munitions, batteries and the like, is not feasible; and even when it is feasible, it requires continuous high energy cooling, which taxes other ancillary engineering systems typical in missiles, aircrafts, railroads, trucks, automobiles, guns, nuclear reactor systems, related combat systems, as well as commercial systems and technology.
The heat sinks of the prior art generally employ phase change material compositions (PCMs) for the absorption and dissipation of heat. The conventional PCM materials are largely solid or fluidic in nature, i.e. liquids, quasi-liquids, or solids such as waxes or other meltable compositions. However, these conventional PCMs have proven to suffer from many technical problems, as well as problems in their use and application. These problems include relatively low latent heats of fusion, the inability to control the shape and form of such fluid PCM materials, as well as the unevenness of heating and cooling. Other problems include the need to provide a containment housing and the stress placed on the housing, resulting in frequent rupture and spillage of the PCM; the hazard to life and property due to PCMs"" high heat content and flammability; and lastly, the uneven cooling hysteresis.
In addition, the known PCMs can spill hot fluids onto a human""s skin, resulting in serious third degree bums due to the sticky contact nature of many hot wax and polymer or plastic phase change materials (PCMs) and the high heat and sticky adherence to the skin. Ruptured non-Composite Fabric Endothermic Material (CFEM) or liquified bulk PCM disks spill their content and cause flash fires, which spread as the PCM pours out during heating in ovens and wax-filled disks are prone to fires, which can spread and flow out of stoves.
Applicant has addressed some of these and other PCM problems in his, U.S. Pat. No. 4,446,916. Applicant has disclosed what he calls a composite fabric endothermic material (CFEM), providing devices especially suitable as heat sinks for aerospace and military use. The patented CFEM provides an improved heat sink that absorbs heat at the melting temperatures of a compound embedded within a fibrous mesh or matrix. The CFEM preferably comprises a phase change material, which is held by capillary action and chemical adhesion to the fibers of the matrix. As a result a greatly increased surface area for heat transfer is obtained; thus providing for controlled melting and thermal dissipation of the fusion cooling agent.
Applicant has also addressed some of the PCM problems in his pending U.S. patent application Ser. No. 08/811,106, now U.S. Pat. No. 5,709,914, the disclosure and contents of which are incorporated herein as if more fully set forth. Such application addresses the need for an improved recyclable endothermic/exothermic thermal storage method for use in many commercial and civilian applications, particularly for food, home and commercial packaging operations. In this application, improved CFEMs are disclosed, capable of being employed in a variety of commercial applications such as in the food industry where a need has arisen for heat retaining or heat insulating containers, packages and thermal storage devices.
However, the active agents suggested in Applicant""s pending U.S. patent application Ser. No. 08/811,106, now U.S. Pat. No. 5,709,914 are not useful in the present inventive heat absorbing devices, as they are concomitantly both endotherms and exotherms. i.e. first, they absorb heat and then they give off heat to the item in connection with which they are being used, for the purpose of maintaining it warm.
While they can accomplish some protection from high temperatures through the physical phenomenon of the absorption of their latent heat of fusion, wherein the appropriate crystalline substance absorbs a quantity of heat to melt without a temperature rise to its surroundings, they are totally unsuitable for applications relating to the absolute protection of heat sensitive devices from high heat. After all, the heat they have absorbed, they must release. In other words, not only do they absorb heat but they also release heat, particularly when confined in a closed environment.
Another problem with the active agents of Applicant""s, U.S. pending patent application Ser. No. 08/811,106, now U.S. Pat. No. 5,709,914 and the prior art PCMs is that they are not capable of absorbing more than 200 cal/gm. Thus, they can remove heat for only a short period of time relative to mass and only at temperatures not exceeding 326xc2x0 F. Consequently, they are not effective for applications requiring cooling at very high temperatures and for long periods of time as would be needed, for example, in airplane and railroad crash recorders, missile electronics, spacecraft devices, power supplies, data recorders employed as aircraft and railroad components and combat devices, and in commercial uses such as oven sensors, fire walls, nuclear reactors, munitions"" boxes, chemical containers, batteries and automobile exhaust systems.
Finally, these latent heat of fusion agents (PCMs) tend to bum at relatively high temperatures raising the overall heat content of the system. In addition, the reversibility of the phenomena virtually guarantees that these agents will also transfer heat into the heat sensitive devices once said devices are at a lower temperature than the respective temperatures of the agents. Consequently, not only do these agents operate as heat absorbing agents, but in closed environments they also operate as heat transfer agents to cause the very damage to the heat sensitive devices that these agents were intended to protect in the first place. This they do by re-releasing the absorbed heat to the heat sensitive device, thereby increasing the time or duration that the heat sensitive device is exposed to a high heat environment.
It is, therefore, the object of the present invention to overcome the disadvantages set forth above and, in particular, to provide for nonreversible heat absorbing applications.
It is a further object of the present invention to provide improved coolant media for use in heat sensitive devices such as airplane and railroad crash recorders, missile electronics, munitions boxes, clothing, firewalls, safe boxes, nuclear reactors, laser shields, thermal pulse shields, spacecraft devices, power supplies, data recorders employed as aircraft and railroad components, combat devices, as well as in commercial uses such as oven sensors and the like.
It is another object of the present invention to provide heat absorbing agents for use in heat sensitive devices, said heat absorbing agents being capable of absorbing heat at temperatures above 300xc2x0 F.
It is another object of the present invention to provide heat absorbing devices with mechanisms that utilize the chemical reactions of latent heat of formation, decomposition or dehydration in such mechanisms.
These objects as well as others will be found in detail in the disclosure that follows below.
According to the present invention a heat absorbing device and method are provided comprising endothermic agents capable of absorbing heat for the cooling and maintenance of the temperature of heat sensitive devices at acceptable levels. Such endothermic agents comprise certain acids and their salts, certain bases and their salts, certain hydrate salts and certain organic compounds. This means that they absorb large quantities of heat to decompose or to dehydrate to either new and simpler, chemically stable chemical compounds, or to their individual component elements.
This ability to absorb heat and irreversibly decompose makes them ideal for the thermal protection of heat sensitive devices in applications where the integrity of the heat sensitive devices must be maintained, under exposure to specified conditions of extreme high heat.
The shape, size and physical characteristics of the heat absorbing devices and likewise the steps of the method are dictated by the type of the heat sensitive device being protected, the heat sensitive device""s spacial limitations, the heat sensitive device""s physical environment and the heat generating conditions, to which the heat sensitive device will be subjected.
Similarly, the type and the amount of endotherms used in the heat absorbing device and in the method are dictated by the heat sensitivity of the heat sensitive device; the maximum temperature at which the heat sensitive device can continue to be viable at; the extreme temperatures, to which the heat sensitive device will ultimately be subjected; the time for which the heat sensitive device will be exposed to said extreme heat generating conditions; and the total thermal flux or thermal load, to which the heat sensitive device will be subjected.
Preferably, the endotherms can be boric acid; metal hydroxides and their mixtures; carbonates and bicarbonates and their mixtures; salts of acetic acid, salts of formic acid, salts of boric acid, and their mixtures; paraldehyde, paraformaldehyde, and trioxane and their mixtures; and hydrate salts and their mixtures. Further such endotherms can be supported within the device, via a(n) retaining matrix, packaging, encapsulation, microencapsulation, enclosure or structure to form a heat absorbing surface, device or structure.
The heat sensitive devices can be embedded within the endotherms; or they can be surrounded by the endotherms; or the endotherms can line the walls (inner or outer) of the closed container within which the heat sensitive device is placed; or in the alternative, the endotherms can be adhered to a substrate (flexible or non-flexible) capable of being adapted to the size and shape necessary for use with said heat sensitive devices.